What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
Unfortunately, this is not possible in the Paypal Integration. A workaround for this would be to setup your product items using Radio Button (single selection) or Checkbox (multi selection) or Dropdown (single/multi selection).
You can assign a value for each option (http://www.jotform.com/help/301-How-to-Assign-Calculation-Value).
Then you can calculate it in the form (http://www.jotform.com/help/259-How-to-perform-calculation-in-the-form).
After that, you can pass the total to Paypal (http://www.jotform.com/help/275-How-to-pass-a-calculation-to-a-payment-field).
Please try that and let us know if you need help with the workaround.